(a) Field of the Invention
The present invention relates to polyalkylsilsesquioxane particulates and a method of preparing the same, and more particularly to polyalkylsilsesquioxane particulates that can be used as a diffusing agent or various additives because of their low moisture content and low content of surface silanol groups, and a method of preparing the same.
(b) Description of the Related Art
Since polyalkylsilsesquioxane particulates have a cross-linked structure of a dense 3-dimensional network, the particulates have a low specific gravity in comparison with an organic polymer and there is no gravimetric change until 400° C., and moreover the particulates have excellent heat-resisting property and mobility.
Polyalkylsilsesquioxane has been generally known since soluble polyphenylsilsesquioxane was first synthesized in the nineteen-sixties by Brown, Jr. et al. of GE Co., Ltd. Polyalkylsilsesquioxane is a common name of all compounds having an empirical formula of RSiO3/2, wherein R is hydrogen, an arbitrary alkyl, an alkylene, an aryl, an arylene, or organic functional derivatives including the same.
As a method of preparing the polyalkylsilsesquioxane particulates, which are well known as silicone resin powder, a method of hydrolyzing and polycondensing a tri-functional silane, such as an organotrichlorosilane and an organotrialkoxysilane, was suggested.
Japan patent publication Hei 4-70335 discloses a method of hydrolyzing and polycondensing a methyltrialkoxysilane and/or a partial hydrolysis-condensate thereof and ammonia or an aqueous solution of an amine while slowly stirring it so as to maintain a layered state, in which the methyltrialkoxysilane and/or the partial hydrolysis-condensate thereof constitutes the upper layer. However, it is very difficult to control the stirring speed and maintain the interface of the hydrolysis-polycondensation reaction in such method, and the method has a disadvantage in that the efficiency of production in terms of polymerization time and device volume is low because there is little occasion for contacting with an alkali and thus the reaction speed is slow.
Korea patent publication No. 1993-0006260 discloses a method of hydrolyzing an organotrialkoxysilane in the presence of an organic acid, adding a solution of water/alcohol and subsequently a basic aqueous solution thereto, and condensing the same in a stationary state. By such method, particulates that do not form coagulations can be obtained with a low concentration of catalysts, but it is not suitable for producing particulates having a diameter of 1 μm or more.
Korea patent publication No. 1998-0024929, also, discloses a method of hydrolyzing and condensing an organotrialkoxysilane in an aqueous solution including an anionic surfactant, a polymer stabilizing agent, and a hydroxyl base. In the method, particulates that do not form coagulations can be obtained with a low concentration of catalysts by adding a dispersing stabilizer, but it is difficult to obtain reproducibility of the prepared particle size with a low concentration of catalysts, and the method has disadvantages in that the efficiency of production is low because the organotrialkoxysilane, which is a solid part of the raw material, cannot be used much in order to prevent the formation of coagulations, and the amount of residual silanol is substantial.
To solve the problems, Japan patent publication Hei 2-150426 discloses a method of treating the surface of polymethylsilsesquioxane particulates with a silylating agent including polyfluoroalkyl groups, and Japan patent publication Hei 3-244636 provides a method of treating the surface of silsesquioxane particulates with hexamethyldisilazane and/or divinyltetramethyldisilazane in water. However, the silicone particulates obtained by these methods are not sufficiently improved in terms of water repellency and need to be handled with care during the storage of products because their hygroscopic property in storage is increased.
Therefore, when the polyalkylsilsesquioxane particles prepared by the prior arts are mixed and used with various rubbers or plastics, the problem of a high hygroscopic property in storage may be caused because the water repellency thereof is low and the moisture content is high because of the silanol groups on the surface of the polyalkylsilsesquioxane particles.